Devices that emit sounds to track medical status or pinpoint military targets may cause mistakes

March 31, 2002

WASHINGTON -- From the classroom to the cockpit, a burgeoning number of devices use sound -- whether in the form of beeps, clicks, alarms or tones -- to tell people what's happening in bodies, structures and machines. These devices translate data changes into corresponding sound changes, guiding everyone from nurses and surgeons to jet pilots -- sometimes in critical or life-threatening situations. However, new research reveals that people misperceive how sounds change when both their pitch and loudness change, as often happens with these devices. Listeners can't accurately judge how the sounds' changes reflect changes in the underlying data -- and may, as a result, make serious mistakes. The research appears in the March issue of the Journal of Experimental Psychology: Applied.

Devices that "sonify" data have expanded beyond the well-known Geiger counter, which warns about radioactivity by clicking more rapidly as it gets closer to nuclear material. These devices appear in an array of settings, warning fighter pilots of target and threat locations, evaluating the structural integrity of large bridges, guiding the manipulation of surgical instruments during brain surgery, and more. Say authors John Neuhoff, Ph.D., Gregory Kramer, Ph.D., and Joseph Wayand, M.A. (a Ph.D. candidate), sonification devices appear everywhere from anesthesiology stations (for one, a heart monitor might beep more quickly or emit a constant tone when a patient is in danger) to factory production-controls, stock-market trading floors and data displays for visually impaired people.

However, despite their proliferation, the effectiveness of these devices has not been fully evaluated. Neuhoff et al., concerned about the growing suspicion that, "changes in one variable may influence the perception of changes in another variable, leading to distorted perception of the underlying data," conducted three experiments.

Participants listened to a tone that got either higher or lower in frequency (changed pitch) and, at the same time got either louder or softer. Listeners, as they would in real life, estimated the amount of change in both pitch and loudness. They also estimated changes as the sounds changed in duration and complexity -- again, reflecting the real-world demands of sonification.

Neuhoff et al. found a substantial perceptual interaction. Listeners did not correctly gauge changes in pitch and loudness, depending on how the two stimuli changed in relation to each other. For example, when pitch and loudness changed in the same direction (both rising or falling), listeners perceived an overall change as greater than when they changed in opposite directions. Also, sounds that increased in loudness were perceived to change more than those that decreased, despite the same amount of intensity change.

Listeners also responded to a stock-trading display in which sound changes were said to track stock prices and trading volume. The perceptual interactions persisted in this more realistic situation. In short, listeners couldn't perceive changing stimuli accurately, because the presence of other changing stimuli distorted their perception.

Neuhoff et al. remark that their results have practical significance, especially in light of the interaction's magnitude. "Distortions of the data underlying an auditory display," they write, "could have grave real-world consequences." They urge researchers to further study perceptual interaction, in order to create more effective sonification techniques -- particularly in situations that demand precision.

The researchers also draw on their findings to propose that duplicate mapping of frequency and intensity onto the same data variable may help to improve performance. For example, a sound could both get louder and pulse faster for the same critical indicator, such as a blood flow in the heart.
Article: "Pitch and Loudness Interact in Auditory Displays: Can the Data Get Lost in the Map?" John G. Neuhoff, Ph.D., The College of Wooster; Gregory Kramer, Ph.D., Metta Foundation; Joseph Wayand, M.A., Kent State University; Journal of Experimental Psychology - Applied, Vol 8. No.1

(Full text of the article is available from the APA Public Affairs Office)

John Neuhoff can be reached by email at or by phone at (330) 263-2475. The College of Wooster is in Wooster, Ohio.

The American Psychological Association (APA), in Washington, DC, is the largest scientific and professional organization representing psychology in the United States and is the world's largest association of psychologists. APA's membership includes more than 155,000 researchers, educators, clinicians, consultants and students. Through its divisions in 53 subfields of psychology and affiliations with 60 state, territorial and Canadian provincial associations, APA works to advance psychology as a science, as a profession and as a means of promoting human welfare.

American Psychological Association

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